Line a baking sheet with parchment paper and then lightly spray with non-stick cooking spray. Set aside.
Melt chocolate in a double boiler. I used a bowl placed over a pot of boiling water to do this. Stir constantly until smooth.
When the chocolate is completely melted, add the espresso powder and stir well.
Add 3/4 cup of the nuts and mix in with the chocolate.
Pour the chocolate and nut mixture on to parchment lined cookie sheet.
Spread with an offset spatula to about 1/4 in thickness.
Sprinkle the remainder of the nuts over the top of the bark. Sprinkle lightly with sea salt.
Place in refrigerator to harden.
Once hard, break it into small pieces and store in an airtight container.
Bark will remain fresh up to a week.